take a look at this wasteland that used to be a neighborhood. now, people who live down there still aren't allowed to go back in. instead, it's filled with investigators who are still trying to figure out exactly why this happened. the natural gas pipe that leveled this neighborhood was packed up and trucked out by the ntsb today as their most critical piece of evidence, even as neighbors just down the street are finally returning home. >> what the [ bleep ] happened? >> reporter: the people who live on the street where this incredible home video was taken are still nervous, and the sight of pg&e workers using electronic sniffers to check for more leaks under their street isn't helping. >> i feel secure, but she's not. she's scared. she keeps telling me, "i don't wanna come home, mom, i don't wanna go home." >> reporter: investigators so far have two areas of concern as they examined the pipe which was first installed in 1956. first, that it has a long seam where it was welded together and may have been susceptible to corrosion. but they've also